This invention relates to the art of sterilization in general and, in particular, to a method of sterilizing food packaging materials, food packages, or comparable objects by dual agents. The invention also particularly concerns an apparatus for sterilizing, typically, a continuous strip of food packaging film in accordance with the inventive method.
Chemical sterilization and physical sterilization represent two broad categories into which there can be classified various known methods of destroying microbial life on and in an object such as food packages. Chemical sterilization involves the use of such chemical substances as ethylene oxide, propylene oxide, and hydrogen peroxide. The gases of the first named two compounds have good sterilizing effects and permit, as an additional advantage, easy application to completed packages. These gases are toxic, however, inviting an objection if not thoroughly removed from the packages after treatment. Hydrogen peroxide, on the other hand, has recently been reported to be a possible cause of cancer, and this has doomed its use as a sterilizer in the food processing or manufacturing industry.
Although a myriad of other known bactericidal or disinfectant chemicals do exist, each has some drawback or another, such as toxicity or low sterilizing ability. None is quite suitable for the sterilization of food packages.
Radiation sterilization means the irradiation of the object with gamma rays, ultraviolet radiation, etc. Gamma rays permeate plastics and so, like the above noted gases, can sterilize food packages of such material in their final phase of fabrication. This advantage is offset, however, by the fact that gamma rays impair the heat sealing strength of the irradiated material and, when applied to plastic films or the like, cause discoloration.
Ultraviolet rays are less hazardous to man, and therefore are easier to handle, than other forms of radiant energy. They also leave no residue on the irradiated object. However, ultraviolet radiation possesses the drawback of acting on exposed surfaces only; even dust particles on the irradiated surfaces shield the underlying surface portions from the rays, obstructing their complete sterilization.
As may have been understood from the foregoing consideration of the prior art, the conventional methods of sterilization all have one problem or other. None is self-sufficient for the sterilization of food packaging materials, food packages or like objects.